Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA, United States of America.
Phys Med Biol. 2020 Jul 8;65(14):145001. doi: 10.1088/1361-6560/ab9981.
In proton-based radiotherapy, proton radiography could allow for direct measurement of the water-equivalent path length (WEPL) in tissue, which can then be used to determine relative stopping power (RSP). Additionally, proton radiographs allow for imaging in the beam's-eye-view. In this work, a proton radiography technique using a flat-panel imager and a pencil-beam scanning (PBS) system is demonstrated in phantom. Proton PBS plans were delivered on a Varian ProBeam system to a flat-panel imager. Each proton plan consisted of energy layers separated by 4.8 MeV, and a field size of 25 cm × 25 cm. All measured data is binned into a layer-by-layer delivery in post processing. To build a calibration curve correlating detector response to WEPL, the plans were delivered to slabs of solid water of increasing thickness. Pixel-by-pixel detector response in the time/energy domain is then fit as a function of WEPL. Tissue equivalent phantoms are imaged for evaluation of WEPL accuracy. A spatial resolution phantom and a head phantom are also imaged. For all experiments, the detector was run with an effective pixel size of 0.4 mm × 0.4 mm. The proposed method reconstructed RSP with mean errors of 2.65%, -0.14%, and 0.61% for lung, soft tissue, and bone, respectively. In a 40 mm thick spatial resolution phantom, a 2 mm deep pinhole with 1 mm diameter can be seen. The accuracy and spatial resolution of the method show that it could be implemented for patient position verification. Further development could lead to patient-specific verification of RSP to be used for treatment guidance.
在质子放射治疗中，质子射线照相术可以直接测量组织中的水等效路径长度 (WEPL)，然后可以使用该 WEPL 来确定相对阻止本领 (RSP)。此外，质子射线照相术允许在射束视线内进行成像。在这项工作中，在体模中演示了一种使用平板成像仪和铅笔束扫描 (PBS) 系统的质子射线照相术技术。质子 PBS 计划在瓦里安 ProBeam 系统上递送到平板成像仪。每个质子计划由 4.8 MeV 分离的能层组成，并且射野大小为 25 cm × 25 cm。在处理中，所有测量数据都按层进行分层交付。为了建立与 WEPL 相关的探测器响应校准曲线，将计划递送到厚度不断增加的固体水块。然后，根据 WEPL 将时间/能量域中的每个像素的探测器响应拟合为函数。为了评估 WEPL 精度，对组织等效体模进行成像。还对空间分辨率体模和头部体模进行成像。对于所有实验，探测器的有效像素尺寸为 0.4 mm × 0.4 mm。对于肺、软组织和骨骼，所提出的方法分别重建 RSP 的平均误差为 2.65%、-0.14%和 0.61%。在 40 mm 厚的空间分辨率体模中，可以看到 2 毫米深的 1 毫米直径的小孔。该方法的准确性和空间分辨率表明，可以将其用于患者位置验证。进一步的开发可以导致用于治疗指导的 RSP 的患者特异性验证。
